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https://issues.apache.org/jira/browse/SPARK-24957?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dongjoon Hyun updated SPARK-24957:
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Affects Version/s: 2.0.2
> Decimal arithmetic can lead to wrong values using codegen
> ---------------------------------------------------------
>
> Key: SPARK-24957
> URL: https://issues.apache.org/jira/browse/SPARK-24957
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.0.2, 2.1.3, 2.2.2, 2.3.1
> Reporter: David Vogelbacher
> Assignee: Marco Gaido
> Priority: Major
> Labels: correctness
> Fix For: 2.2.3, 2.3.2, 2.4.0
>
>
> I noticed a bug when doing arithmetic on a dataframe containing decimal
> values with codegen enabled.
> I tried to narrow it down on a small repro and got this (executed in
> spark-shell):
> {noformat}
> scala> val df = Seq(
> | ("a", BigDecimal("12.0")),
> | ("a", BigDecimal("12.0")),
> | ("a", BigDecimal("11.9999999988")),
> | ("a", BigDecimal("12.0")),
> | ("a", BigDecimal("12.0")),
> | ("a", BigDecimal("11.9999999988")),
> | ("a", BigDecimal("11.9999999988"))
> | ).toDF("text", "number")
> df: org.apache.spark.sql.DataFrame = [text: string, number: decimal(38,18)]
> scala> val df_grouped_1 =
> df.groupBy(df.col("text")).agg(functions.avg(df.col("number")).as("number"))
> df_grouped_1: org.apache.spark.sql.DataFrame = [text: string, number:
> decimal(38,22)]
> scala> df_grouped_1.collect()
> res0: Array[org.apache.spark.sql.Row] = Array([a,11.9999999994857142857143])
> scala> val df_grouped_2 =
> df_grouped_1.groupBy(df_grouped_1.col("text")).agg(functions.sum(df_grouped_1.col("number")).as("number"))
> df_grouped_2: org.apache.spark.sql.DataFrame = [text: string, number:
> decimal(38,22)]
> scala> df_grouped_2.collect()
> res1: Array[org.apache.spark.sql.Row] =
> Array([a,1199999999948571.4285714285714285714286])
> scala> val df_total_sum =
> df_grouped_1.agg(functions.sum(df_grouped_1.col("number")).as("number"))
> df_total_sum: org.apache.spark.sql.DataFrame = [number: decimal(38,22)]
> scala> df_total_sum.collect()
> res2: Array[org.apache.spark.sql.Row] = Array([11.9999999994857142857143])
> {noformat}
> The results of {{df_grouped_1}} and {{df_total_sum}} are correct, whereas the
> result of {{df_grouped_2}} is clearly incorrect (it is the value of the
> correct result times {{10^14}}).
> When codegen is disabled all results are correct.
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